After respiratory syncytial virus (RSV) circulation was suppressed early in the COVID-19 pandemic, the number of admissions to Canadian pediatric hospitals more than doubled after public health restrictions were lifted, a team led by McGill University researchers report today in CMAJ.
The team conducted surveillance to compare hospitalization and intensive care unit (ICU) admission rates of infants and children aged 0 to 16 years at 13 Immunization Monitoring Program, Active (IMPACT) centers in Canada in 2022-23 with those from two prepandemic seasons (2017-18 and 2019-20).
In North America, RSV is the leading cause of hospitalization in children in their first year of life, with healthy, full-term infants making up 77% to 88% of pediatric RSV hospitalizations. It poses the highest risk of severe disease in the second and third months of life, declining thereafter, senior author Jesse Papenburg, MD, an infectious disease specialist at the Montreal Children’s Hospital, told CIDRAP News.
“As babies grow, they're better able to handle the RSV infection if it gets down in the lungs,” he said. “And as they get into their second or third year of life, they may have had a previous RSV infection that gives them some degree of immunity to help fight it off and maybe keep it up in the upper respiratory tract, just causing a cold and not bronchiolitis or pneumonia.”
Youngest group made up 62% of ICU admissions
During the 2022-23 season, there were 5,362 RSV pediatric hospital admissions, including 1,260 (23.5%) ICU admissions, both more than double the prepandemic yearly averages. The percentage of RSV hospitalizations among all-cause admissions rose 3.5 percentage points, to 6.8%.
Papenburg said that pandemic-era public health measures enacted to curb COVID-19 transmission also slowed the spread of other respiratory viruses, such as RSV, in Canada.
“In the 2020-21 winter, we had almost no RSV circulation and almost no hospitalizations due to RSV,” he said. Thus, “as public health measures were eventually lifted, there was more population mixing, and with the accumulation of susceptibles [vulnerable patients] over a year or two, when the virus got into the community, it was able to spread much more easily.”
The median patient age climbed from 6 to 9 months over the study period. In total, 41.5% of RSV hospital admissions were in infants younger than 6 months. Those young children also accounted for 62.1% of ICU admissions. While the ICU proportion stayed stable, the likelihood of ICU admission in this age-group increased relative to prepandemic seasons (adjusted odds ratio, 1.35).
While infection numbers rose two to three times the prepandemic totals in all age-groups, the youngest children were the most vulnerable when community infections increased, Papenburg said.
Uneven access to prevention across Canada
The weekly 2022-23 RSV incidence peaked sooner and higher and lingered longer than expected from moving-average time-series analyses. “I don't want to speculate about the causes, but I think that the reason that we saw more heterogeneity across provinces or across regions in Canada has to do with the stringency and the timing of stringency of COVID-19 pandemic measures,” Papenburg said.
Increased and equitable implementation of novel RSV immunization strategies to protect young infants nationwide has the potential to have a substantial public health impact, given the persistently high RSV burden in infants younger than 6 months.
He recommends infant immunization with a dose of long-acting monoclonal antibodies, which can reduce the risk of medically attended RSV by over 80%, or maternal RSV vaccination during pregnancy, which can reduce the risk of infant hospitalization by 50% to 70%.
“Since their approval in Canada in 2023 and 2024, implementation of highly effective RSV immunoprophylaxis with long-acting monoclonal antibodies and vaccination during pregnancy has varied across provinces,” the authors wrote.
“Increased and equitable implementation of novel RSV immunization strategies to protect young infants nationwide has the potential to have a substantial public health impact, given the persistently high RSV burden in infants younger than 6 months,” they concluded.
